diff --git a/main.js b/main.js
index b9d8c1d..2929dd5 100644
--- a/main.js
+++ b/main.js
@@ -5,12 +5,18 @@ import { compute } from "./modules/compute.js";
 function evaluate() {
 	const expr = document.querySelector("#expr");
 	const modulus = document.querySelector("#modulus");
+	const result = document.querySelector("#result");
+
 	const m = BigInt(modulus.value);
+	if (m === 0n) {
+		const e = Error("modulus cannot be 0")
+		result.value = e;
+		console.log(e);
+		return;
+	}
 
 	const tokens = tokenize(expr.value);
 	console.log(tokens);
-
-	const result = document.querySelector("#result");
 	let queue = [];
 	try {
 		queue = shunt(tokens);